UCSB EEMB 2 - Lec #15 EEMB 2 SM17 1S (Speciation) (14 pages)

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Lec #15 EEMB 2 SM17 1S (Speciation)



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Lec #15 EEMB 2 SM17 1S (Speciation)

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Pages:
14
School:
University of California, Santa Barbara
Course:
Eemb 2 - Introductory Biology III

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Speciation The Evolutionary Process Variation Natural Selection 1 Variation 2 Natural Selection 3 Genetic Divergence 4 Reproductive Isolation 5 Speciation Genetic Divergence Reproductive isolation Speciation Speciation Speciation 1 75 million species have been identified Changes in allele frequencies that are significant enough to mark the formation of daughter species from parent species Species How do we define a species Phylogeny line of descent Sp F Sp A Sp B Sp C Sp D Sp E Ex Poison dart frogs Dendrobates pumilio N S Leopard frogs Speciation Speciation 1 Biological Species Concept Ernst Mayer 1942 Species are groups of interbreeding natural populations that are reproductively isolated form other such groups the capacity to contribute to a shared gene pool is qualification for species membership Limitations this concept does not apply to asexually reproducing organisms bacteria some species of plants and fungi Western Meadowlark Eastern Meadowlark Ex Speciation Speciation 2 Morphological species concept based on morphological structural characteristics can be applied to sexual and asexual organisms Limitations Variation in morphology ontogenetic niche shifts sexual dimorphism makes this definition difficult Ex Bacteria Butterflies 3 Paleontological Species Concept Species are morphological discrete groups known only from the fossil record Limitations limited evidence not all organisms fossilize well Speciation Speciation 4 Ecological Species Concept Leigh Van Valen 1976 Species are separated by their ecological niche Limitations niche is hard to define and often flexible 5 Phylogenetic Species Concept Species are sets of organisms with a unique genetic history compares physical characteristics molecular sequences with those of other organisms limitations at what difference do we define a species It is not easy to define a species and there are multiple techniques to do so Method dependent on species under investigation Speciation Mechanisms of Speciation Speciation due to accumulation of genetic changes that promote significant differences between populations Depends on how gene flow between populations is interrupted Primary mechanisms of speciation 1 speciation due to abrupt events Ex changes in chromosomal 2 speciation due to adaptation to different environments RIMs Speciation Mechanisms of Speciation 1 Allopatric Speciation Gene flow is interrupted when a physical barrier between populations occurs that promotes the genetic changes necessary for speciation Physical barrier is effective at blocking gene flow between pops and depends on organisms ability to migrate Reproductive isolation arises in the genetically diverging populations Speciation is complete when individuals of the 2 populations can not interbreed mutation natural selection genetic drift promote genetic divergence Speciation Mechanisms of Speciation 1 Allopatric Speciation Physical barriers lead to reproductive isolation Small isolated populations are more likely than large



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